There is a suggestion that a beta type zeolite having undergone ion exchange with iron ions may be used as a catalyst for cleaning exhaust gas from automobiles (refer to Patent Documents 1 to 3). For example, Patent Document 1 discloses a denitration catalyst containing a support that is obtained by exchanging ions of a beta type zeolite in which a molar ratio of SiO2/Al2O3 is 15 to 300 with Fe3+ ions in an amount of 0.1% by mass to 15% by mass, and ferric oxide that is supported on the support.
Patent Document 2 discloses a process of performing ion exchange of a beta type zeolite, which has a skeleton structure where the content of Si belonging to Q4 of a zeolite structure observed in a 29Si MAS NMR spectrum is 35% by mass to 47% by mass and in which a molar ratio of SiO2/Al2O3 is equal to or higher than 20 and less than 100, so as to cause Fe3+ to be supported on the zeolite, and bringing the zeolite into contact with exhaust gas containing nitrogen monoxide.
Patent Document 3 discloses a method for producing a NOX adsorbent. This method includes an impregnation step for preparing an iron chloride-containing zeolite by impregnating a beta type zeolite with an aqueous iron chloride solution, an ion exchange step for heating the iron chloride-containing zeolite at 330° C. to 500° C. in a moisture-free atmosphere so as to cause ion exchange by using Fe, and a thermal treatment step for thermally treating the iron chloride-containing zeolite obtained after the ion exchange step in a non-oxidizing atmosphere.